An electronic apparatus includes a switching power supply that supplies a load with power. The switching power supply is, for instance, a DC-DC converter that converts a DC voltage into another DC voltage. An electronic apparatus that includes various voltage sources with different voltage values may include multiple DC-DC converters for respective voltage sources. It is important to start up the multiple voltage sources in an appropriate order when an electronic apparatus is started, and to stop the multiple voltage sources in an appropriate order when the electronic apparatus is stopped. If the order of stating the voltage sources in the start sequence is inappropriate or the order of stopping the voltage sources in the stop sequence is inappropriate, the electronic apparatus may malfunction. For instance, a state may be maintained where a forward bias is applied to the p-n junction of a semiconductor device that is an element of an electronic apparatus, and unnecessary current may continue to flow (which is referred to as a latch-up phenomenon).
Thus, a method has been proposed that quickly reduces the output voltage of a DC-DC converter after the DC-DC converter is stopped (e.g., Japanese Patent Laid-Open No. 2006-109535, Japanese Patent No. 4621448). For instance, a soft stop technique has been proposed that provides an external capacitor and a discharging resistor are provided, and reduces the output voltage after a DC-DC converter is stopped. According to the soft stop technique, after the DC-DC converter is stopped, a charge accumulated in the capacitor starts to be discharged from the discharging resistor, and a terminal voltage of the capacitor is input into an error amplifier circuit. Accordingly, in the error amplifier circuit, a reference voltage to be compared with the output voltage gradually decreases, thereby allowing the output voltage of the DC-DC converter to gradually decrease. Furthermore, another technique is proposed according to which, in a synchronous rectifying DC-DC converter, after the DC-DC converter is stopped, a transistor on a main side is turned off while a transistor on a synchronous side is turned on, thereby allowing a charge accumulated in a capacitance element, such as an output capacitor, provided on a load side to be rapidly drawn, and allowing the output voltage to quickly decrease.